Why is it recommended not to wear a surgical mask for more than 4 hours?
Text updated on 2020-10-21
In some countries, it is advised to change your surgical mask every 4 hours. This maximum duration of 4 hours comes from a WHO report and a study on the tolerance time of the mask. In reality, the surgical mask can be worn longer.
In some countries such as France or Australia, it is recommended not to use a surgical mask for more than 4 hours. Why this 4-hour limit?
This 4-hour maximum duration of mask use seems to come from a World Health Organization (WHO) recommendation given in March 2020, itself based on a 2009 study which showed that after 4 hours, the acceptability and tolerance of the mask by healthcare personnel begins to decrease.
When the mask is no longer tolerated, there will be a tendency to touch it often with one's hands, which increases the risk of contact contamination, and to reposition it on one's face, which increases the risk of inhaling viral particles. In addition, when the mask is wet, its electrostatic properties decrease (therefore it retains less particles), and its air permeability decreases (therefore it is less "breathable"). This is why it is then preferable to change the mask.
In fact, surgical masks and N95 retain their filtration properties for more than 4 hours. It is therefore possible to wear your mask for more than 4 hours and change it only:
- when it is no longer tolerated or accepted
- when the filtering part of the mask is wet...
- when the mask has lost some of its integrity: relaxed elastic, damaged filtering part.
- when there were potentially infectious droplets splashing onto the mask.
If you don't talk and don't make an effort, the mask stays dry for a long time and you can keep it on. If you speak loudly or sing, if you exert yourself, or if it is very hot, the mask gets wet quickly and it is best to change it regularly.
To limit plastic pollution, we recommend that surgical masks be reused after leaving them in paper envelopes for a week. A wet mask will therefore have time to dry well before being reused. See the question COVID : Can a surgical mask be used more than once?
Look out! This text concerns only surgical masks, for which there have been many scientific studies.
The WHO report of March 2020 on the rational use of protective equipment states that "the use of a single respirator for more than 4 hours can cause discomfort and should be avoided". It states that "respirators" (e.g., N95, FFP2 or equivalent standard masks) have been used for a prolonged period of time in previous public health crises involving acute respiratory diseases, when there was a lack of protective equipment. This involves wearing the same respirator when caring for several patients with the same diagnosis without removing it, and there is evidence that respirators retain their protection when used for prolonged periods of time.World Health Organization. (2020). Rational use of personal protective equipment (PPE) for coronavirus disease (COVID-19): interim guidance, 19 March 2020 (No. WHO/2019-nCoV/IPC PPE_use/2020.2). World Health Organization.
The WHO report of March 2020 cites this article to justify the low tolerance of masks after 4 hours. The median reported tolerance is 7.7 hours for a surgical mask and 5.8 to 6.6 hours for an N95 mask.Radonovich LJ Jr, Cheng J, Shenal BV, Hodgson M, Bender BS. Respirator tolerance in health care workers. JAMA. 2009;301(1):36-8. doi:10.1001/jama.2008.894.
The WHO report of April 2020 (the most recent) on the rational use of protective equipment no longer mentions the 4-hour limit.World Health Organization. (2020). Rational use of personal protective equipment for coronavirus disease ( COVID-19) and considerations during severe shortages: interim guidance, 6 April 2020 (No. WHO/2019-nCov/IPC_PPE_use/2020.3). World Health Organization.
In France, the official recommendation is not to use a surgical mask for more than 4 hours.Ministry of Solidarity and Health. Recommendations for the use of face masks in the context of a progressive process of deconfinement. 06/05/2020.
The New South Wales Clinical Excellence Commission in Australia recommends changing the mask when it has been worn for 4 hours. It is specified that the use of a mask for more than 4 hours is likely to be poorly tolerated (increased risk of self-contamination).Clinical Excellence Commission, New South Wale Government. COVID-19 Infection Prevention and Control. Application of PPE during COVID-19. Version 2.3 - August 2020.
Oxford University Hospitals and the NHS in the UK do not mention a maximum limit on the time a mask can be used.COVID-19 staff faqs: wearing face masks in our hospitals. Oxford University Hospitals.
This U.S. CDC guide states that workers in other industries routinely use N95 respirators for several hours without interruption. Experience in these settings indicates that respirators can function properly for up to 8 hours of continuous or intermittent use. Some studies have used health care workers as test subjects and many of these subjects have successfully worn an N95 respirator on the job for several hours before having to remove it. Thus, the maximum duration of continuous use in dust-free healthcare workplaces is generally dictated by hygiene concerns (e.g., the respirator was discarded because it was contaminated) or practical considerations (e.g., need to use the bathroom, meal breaks, etc.), rather than by a predetermined number of hours.Centers for Disease Control and Prevention. Recommended Guidance for Extended Use and Limited Reuse of N95 Filtering Facepiece Respirators in Healthcare Settings. 2020.
This guide from the New York City Department of Health in the United States indicates that the maximum length of time a mask can be worn permanently is not well-defined and that studies show that N95 masks remain effective for up to 8 hours of continuous use. However, it is mentioned that the tolerance of the person wearing the mask may limit this time to shorter periods.Strategies for Reuse and Extended Use of Personal Protective Equipment (PPE) During COVID-19 Outbreak. New York City Health Department Guide.
The filtration of surgical masks is tested several times after mimicking the use by an alternating air flow. Filtration appears to be little affected by prolonged reuse or multiple 4-hour cycles, but no statistics were used in testing this hypothesis. After 3 cycles, filtration is still about 95%.Song, W., Pan, B., Kan, H., Xu, Y., & Yi, Z. (2020). Heat inactivating and reusing of virus-contaminated disposable medical mask. medRxiv.
The filtration of N95 masks does not decrease after 8 hours of use (table 6).Tsai, P. (2020). Performance of masks and discussion of the inactivation of SARS-CoV-2. Engineered Science, 10(3), 1-7.
Study of 9 nurses working in the intensive care unit of the Louisville hospital who were asked to wear an N95 mask during their 12 hours of work for two days in a row. Each nurse used an average of 3 masks per day. They decided to remove their masks either temporarily to eat or drink (56% of cases), or because the mask had become uncomfortable (22% of cases), or because it was the end of their work day (22% of cases). Nurses of higher weight reported more problems with mask non-tolerance than those of lower weight: physical effort, shortness of breath, discomfort, feeling hot, headaches, dizziness. Physiological measurements (blood pressure, heart rate, CO2, and transcutaneous O2) taken every hour nevertheless showed that long-term use of respiratory protection has no clinical physiological effect. As all 9 nurses were volunteers for this study, it is possible that these nurses have a better tolerance to masks than the general population.Rebmann T, Carrico R, Wang J. Physiologic and other effects and compliance with long-term respirator use among medical intensive care unit nurses. Am J Infect Control 2013;41:1218-23.